The present invention relates to a process for preparing catalysts useful for hydrotreating petroleum fractions. The present invention further relates to new catalysts and to a hydrotreatment process employing such catalysts.
When crude oils are distilled, the different fractions obtained contain amounts of impurities such as sulphur, nitrogen, vanadium, nickel, etc., which vary in amount with the origin of the treated crude. For most further use, these fractions must be improved. Such improvement generally is performed by a hydrogenating catalytic treatment or hydrotreatment. The additional advantage of this hydrogenating treatment is to allow the conversion of heavy fractions into light fractions. The catalysts which are generally so used are those containing an oxide of a Group VIII metal, particularly cobalt or nickel, and/or an oxide of a Group VI B metal, particularly molybdenium or tunsten, and a carrier which most often is an alumina.
For the industrial application of such hydrotreating processes, catalyst life must be as long as possible for economic reasons. Further, it is necessary that the catalyst have a high mechanical strength and a high activity.
Several processes for preparing hydrotreating catalysts are known, and their object generally is to obtain catalysts having a high specific surface or pores of determined sizes. However, comparative experiments with commerical catalysts have shown that the activity of hydrotreating catalysts does not depend only on these physical properties. These experiments have shown that a prominent criteria is the crushing strength and abrasion strength of the catalyst. It has been found that catalysts in the form of beads have more strength and resistance than extruded catalysts. Generally, such catalysts are prepared from alumina beads. The alumina beads are impregnated with the catalytic agents.
Several processes have been proposed for preparing spheroidal alumina particles. One of such process comprises dispersing an alumina hydrosol as droplets into a medium wherein gelling occurs, and thereafter, subjecting the beads which are obtained in the form of alumina hydrogel, to one or more aging treatments in order to obtain beads having a suitable mechanical resistance. According to another known process, an alumina hydrosol is mixed with an ammonium salt and a synthetic polymer or a natural gum, the mixture is dispersed into a water-immiscible medium to form beads and thereafter subjected to an aging treatment. However, these processes have the disadvantage of requiring long treatment times which render them uneconomic. Further, alumina beads prepared by some of the known processes contain high amounts, even excessive sometimes, of impurities which are undesirable when these beads are used as supports for hydrotreating catalysts.
An object of the present invention is to provide a new and simple method of preparing spheroidal catalyst particles using an alumina support.
Another object of the present invention is to provide a method of preparing particles whose catalytic activity is not inhibited by impurities.
A further object of the present invention is to provide a process for preparing catalyst particles having uniform sizes.
Still another object of the present invention is to provide a process for preparing hydrotreating catalysts.
A remaining object of the present invention is to provide a method for preparing hydrotreating catalysts in the form of beads having a smooth surface, high mechanical strength and a high activity.